Radio Frequency Identification (RFID) applications are proliferating as the benefits and economics of automated tracking and identification are being realized by the global community. RFID is the ability to detect, read, and/or write data to and from tags that are affixed to “things.” The cost of the RFID tag is an important consideration underlying adoption of this technology.
There are several categories of RFID tags and readers in use. The predominant technology currently uses passive tags. Passive means that the tags have no battery. They derive power from a reader that transmits electromagnetic energy to the tag, which in turn reflects or modulates the energy signal back to the reader. While passive tags and readers are relatively inexpensive, they have severe limitations dictated by physics. For example, passive tags and readers have a limited range (from 0.1 cm to 6 meters) and are non-operational when blocked or shielded by metal objects, liquids and certain solid materials. In such systems, data rates are limited such that a moving object having a tag affixed to it which needs to be read may not travel in excess of approximately 6 mph “drive-thru” speeds thru portals, conveyors, etc, that is, no more than a brisk walk. Further, passive systems have limited data storage capacity and no sensing capability.
There are also “active” tags that derive their power from incorporated batteries. Such devices add significant value to the process of inventory tracking and In Transit Visibility (ITV) enabling processes such as Total Asset Visibility (TAV). Relative to passive tags, active tags have a greater data acquisition range (0 to 1000 meters). Active tags have the ability to provide Real Time Location System (RTLS) effectively, to automatically provide theft deterrence thru continuous and automatic “presence detecting,” and to enable tracking through processes such as manufacturing, shipping, on trucks, forklift transfer, and warehousing. A disadvantage of active tags is that they cost more than passive tags and this requires that these tags must achieve maximum performance, add value to supply chain management, have useful battery life and permit easy replacement or recharging of batteries, while achieving these goals at absolute lowest cost.
Many active tags simply “beacon” or periodically transmit data, such as tag ID data, ranging from several times per second to once every few minutes. This amounts to a “check-in” function, wherein the tag is letting the reader know “here I am”, and implicitly, the object to which the tag is attached is also within reader range. However, this approach has limitations. In many instances, the continuous battery consumption is prohibitive, since RF data transfer is really only required at change of events, that is, for example, when handling or processing the tagged items. In addition, it is often desired to associate a specific tagged item with a process such that the tagged item can be associated with a specific event, time or operator and beacon tags do not provide this utility. It is often desired to locate a specific tagged item in a situation where many identical items are tagged. It may be desired to be able to change the tag's mode of operation, i.e. turn the beacon mode “OFF” or “ON”, or change the beaconing rate. A specific tag should be able to respond under any of these circumstances. The ability to transfer data from the tag via a medium other than RF signals is also a desirable functionality since many locales and operations (such as aircraft flight) require RF silence.
Therefore, current commercial tags offer secondary triggering or communication modes of operation. “Triggering” is the remotely transmitted command to a tag directing that it execute a function such as “transmit RF, store data, or take a sensor reading”. These secondary modes are restricted to the use of magnetic or RF fields to effect the triggering or communication. RF and magnetic triggered tags have the problem of being non-discriminatory. That is, “singulation”, single tag actuation from amongst many, is not possible, by which is meant that picking one item out of many by trying to communicate with that object's tag by RF is not practicable. This is due to the nature of RF fields; they cannot be restrained to a narrow effective Field of View (FOV) and hence are not tag-specific in the presence of many tags. They are also costly.
Low frequencies (of the electro-magnetic domain) such as 125-134 KHz require very close proximity to actuate the tag response and often will not work at all, well or consistently, where the tag is attached to ferrous objects. Higher frequencies such as 915 MHz also are affected by metal items. Higher frequencies are often reflected, creating a background of RF noise that makes single tag actuation less reliable than is required. Similarly, IR noise such as generated by light, TV appliances (particularly LCD and plasma TVs), and heat sources significantly affect IR tags. All of these triggering mechanisms are large, bulky, and expensive. Handheld triggers or communicators are also large and bulky. Many applications require that the tags and readers comply with Intrinsic Safety requirements. This task is significantly complicated and more costly with low frequency devices due to the necessity for relatively high source power. Additionally, the transfer of data is at relatively low speeds.
Accordingly, there is an unmet need in the art for low cost, active RFID tags that provide accurate, reliable, consistent data transfer, including transfer of sensor data in electro-magnetically noisy environments to permit a wide variety of application for tracking of goods and people, for access control, and for security of use of goods and financial transactions, to name a few.